1. Field of the Invention
This invention relates generally to a direct-current motor, and more particularly to a direct-current motor for controlling outboard engines, for example, in which components of the direct-current motor are allowed to be easily assembled, and the protection of the motor proper and the waterproofing effect of the waterproofing construction of the motor, including motor cords are improved.
2. Description of the Prior Art
In motor boats or small fishing boats, the propeller is submerged into, or lifted from, the water by means of a hydraulic cylinder powered by the hydraulic pressure generated by a hydraulic pump driven by a direct-current motor.
FIGS. 7A and 7B show the operation of outboard engines of different constructions. In FIGS. 7A and 7B, solid lines represent the state where the outboard engines are submerged into the water, while dotted lines represent the state where the engines are lifted from the water. The lifting/lowering of a propeller 2 is effected directly by a hydraulic cylinder 3 powered by the hydraulic pressure fed by a hydraulic pump 4. The hydraulic pump 4 is driven by a motor 5. Numeral 6 denotes an engine, 7 a control relay, which will be described later.
FIG. 8 illustrates a prior-art control unit for lifting and lowering the propeller 2. When a switch 8 is thrown to the UP side or the DOWN side, any one of the two relays 7 is energized. In accordance with the operation of the contact 9 of the energized relay 7, the polarity of the current fed from a battery 10 to the motor 5 is reversed, thus causing a hydraulic cylinder 3 to be controlled to lift or lower the propeller by means of a hydraulic pump 4 driven by the motor 5. In the figure, numeral 62 refers to a power relay, and 63 to a thermal relay, respectively.
The motor 5 driving the hydraulic pump 4, which is installed out of the board as shown in FIGS. 7A and 7B, tends to be splashed with the sea water. To protect the motor from the sea water splashes, therefore, the entire motor 5, including the cord outlet, is usually made into a hermetically sealed waterproof construction.
The cord outlet of the motor 5 used in conventional outboard engines has a waterproof construction as shown in FIG. 9 or FIG. 10.
FIG. 9 is a top view of a motor 5. A space, called a pocket for filling the outlet of a cord 12 with a filling material, is provided in a front bracket 52 to which a sealing case 51 of the motor 5; the space being formed by a grommet 13 into which the cord 12 is inserted, a grommet retaining plate 14 a fixing plate 15, etc. and filled with a filling material 16, such as a resin or an adhesive, so as to embed the cord 12 into the pocket.
In the waterproof construction shown in FIG. 10, a locking claw 17a formed on a front bracket 52 into which a cord 12 is inserted, and a cord insertion hole having a tapered portion is provided inside the front bracket 52. A cap 18 has a catch claw 18a on the inside of the brim thereof and a pushing ring 18b for receiving the cord 12 at the center thereof and pushing the end face of a grommet 19. The grommet 19 having a hole for passing the cord 12 at the center thereof is inserted into the cord insertion hole having a tapered portion inside the front bracket 52. By pushing the end face of the grommet 19 with the pushing ring 18b of the cap 18, the grommet 19 is pushed forward and compressed into the tapered portion of the cord insertion hole provided inside the front bracket 52. As a result, airtightness is maintained among the grommet 19, the cord 12 and the front bracket 52. As the cap is further pushed until the catch claw 18a of the cap 18 is engaged with the locking claw 17a of the front bracket 52, the cap 18 is locked to the front bracket 52.
In the prior-art construction shown in FIG. 9, the filling material 16 has to be heated until it solidifies. In addition, the construction shown in FIG. 9 has a number of disadvantages in terms of both sealing performance and manhours since there can be a run-off of the filling material 16, or an imperfect sealing due to an underfill of the filling material 16.
Furthermore, the construction shown in FIG. 9 involves a filling space, called the pocket, and too small a pocket would make it difficult to fill the pocket with the filling material 16. In this way, the construction shown in FIG. 9 has many drawbacks in terms of workability and design.
The construction shown in FIG. 10, on the other hand, is excellent in workability and design, but requires a shape in which the front bracket 52 protrudes outward. This precludes the use of a waterproof construction of the protruding shape as shown in FIG. 10 in a design having a limited space for providing the motor 5.
To prevent excess current from flowing in the armature coil, external wires are usually connected to brushes via a circuit breaker. In the conventional designs, the circuit breaker is housed in a specially designed case, and the case with the breaker is held by an end bracket via a holding means. This design involves the use of a special case for the circuit breaker, and requires a mechanism for holding the case. All this leads to an increase both in the number of parts and in assembly manhours.
In a direct-current motor, moreover, a brush holder has to be provided in the front bracket 52 by some means or other. In the conventional design, the brush holder is fixedly fitted to the bracket 52 using screws and other fastening means. Such a construction makes the brush holding mechanism unwantedly complex, increasing assembly manhours. To cope with this, efforts have been made to form a bracket 52 for holding brushes by molding a synthetic resin, and providing a brush holder integrally with the bracket 52, as shown in FIG. 32. In FIG. 32, numeral 5 indicates a motor; 51 a motor sealing case; 52 a front bracket; 53 a rotor; 54 a stator; 55 a brush, respectively. With such a construction, however, the bracket could be deformed due to heat when the temperature of brushes making sliding contact with the commutator rises.
Consequently, there is a need for improving the construction of the bracket 52 for holding brushes so that as many direct-current motor components as possible can be housed to make the effective use of the limited space available.
In the examples shown in FIGS. 7A and 7B, if the propeller 2 could not be lowered or lifted for some reason or other, large current might flow in the motor 5, resulting in a burn-out of the motor 5. To prevent such an accident, a thermal relay 63 is provided to detect the temperature rise in the motor 5, as shown in FIG. 8, so that when the temperature of the motor 5 exceeds a predetermined value, the thermal relay 63 is actuated to deenergize the power relay 62 to cut off power supply from the battery 10 to the motor 5. As the motor temperature drops, the thermal relay 63 is automatically reset.
FIGS. 23 through 25 illustrate the construction of the thermal relays based on the prior art. FIG. 23 is a top view, FIG. 24 a side elevation, and FIG. 25 a cross section.
As shown in FIGS. 23 through 25, the thermal relay 63 is fixedly fitted to the side of a metallic brush holder 113 for holding a brush 115 by means of a fixture 114. In the figure, numeral 115 indicates a brush making sliding contact with a commutator in a motor; 117 a brush holding plate.
The above-mentioned construction in which the thermal relay 63 is fitted in close contact with the side of the brush holder can cope with a gradual temperature rise normally encountered during overload operation of during a continuous operation for over predetermined hours. In case the propeller 2 becomes entangled with some foreign matter, causing the motor 5 to be locked, however, the temperature rise of the brush holder 113 could not follow the resulting sharp temperature rise of the brush 115, leading to the seizing of the motor 5 before the actuation of the thermal relay 63.
Furthermore, the method of assembling the commutator in a conventional direct-current motor involves the movement of the brushes outward in the radial direction while compressing the spring. This operation has to be done while pulling the so-called pig tails sideways. This operation is extremely troublesome, deteriorating the efficiency of commutator assembly.